1. Field of the Invention
This invention relates to optical sensor apparatus and to associated means by which to color multiplex optically encoded information signals over a compact fiber optic transmission system, so that an accurate digital representation of a sensed physical parameter is available.
2. Prior Art
In general optical terms, color modulation refers to a technique wherein either of a high-pass, low-pass, or band-pass filter may be utilized to change the color or wavelength of an output optical signal in response to an input physical parameter to be sensed. Briefly, a color modulation system would typically include a source of white or broad-band light that is transmitted to a remote sensor, where it is dispersed by means of a prism, a color filter, a defraction grating, or the like. In response to an input parameter, a small portion of the spectrum of the dispersed light is optically transmitted to a central processor where it is analyzed for spectral characteristics. The spectral characteristics provide an indication of the magnitude of the physical parameter. By way of example, an optical transmission system that utilizes color modulation technique to provide indications of a physical parameter can be found in the copending U.S. patent application entilted METHOD AND APPARATUS FOR A FABREY-PEROT MULTIPLE BEAM FRINGE SENSOR, Ser. No. 005,625 filed Jan. 22, 1979 by the common assignee thereof.
In a binary modulation transmission system, many different output channels and corresponding transmission cables are typically required, with each cable transmitting a respective bit of optically coded information regarding a physical parameter. Consequently, the complexity of such a system may be undesirably increased. Moreover, additional interfacing and signal conversion apparatus may be required, should a digital representation of the physical parameter be desired.
In contrast to the color modulation and binary modulation techniques described above, no prior art is known which shows or suggests an effective technique for color multiplexing optical information signals (that are generated by an optical transducer) on a single optical fiber. In general terms, color multiplexing indicates that different color signals, or optimal frequencies, are transmitted on separate color carriers that are entirely independent of one another. Thus, no prior art is known which discloses means for color multiplexing optical signals, wherein separate optically encoded signals are sent on different color carriers, with each carrier frequency, or color, representing one bit of a binary word that is indicative of a physical parameter sensed by the optical transducer.